Automatic drafting using projected ring of light

ABSTRACT

The disclosure concerns a photoexposure device used in automatic drafting and characterized as forming a movable ring of light at the photosensitive drafting surface, and wherein said ring may be formed by a central mask at the optical axis and an outer mask spaced therefrom to form an aperture ring, the central mask sized in relation to the aperture to substantially eliminate bleeding of light at the ring of light on the drafting surface and toward the edge of the ring, during line drawing.

United States atent [151 3,641,885 Hill Feb. 15, 1972 [54] AUTOMATIC DRAFTING USING 3,548,713 12/1970 Webster ..95/l2 PROJECTED RING OF LIGHT 3,323,414 6/1967 Ritchie et al... ..95/l2 3,330,182 7/1967 Gerber et al ..95/l2 [72] Inventor: Armin J. Hill, Provo, Utah Primary Examiner-Samuel S. Matthews [73] Asslgnee' 2 522:: f Products Assistant ExaminerEdna M. Bero AttorneyWhite & Haefliger [22] Filed: Mar. 29, 1968 [21] Appl. No.: 717,159 [57] ABSTRACT The disclosure concerns a photoexposure device used in autoy matic drafting and characterized as forming a movable ring of [52] US. Cl. .,.95/l, 95/12, 355/20, light at the photosensitive d fti rf and wherein said 355/40, 35 ring may be formed by a central mask at the optical axis and [51] Elli. Cl- ..G03b 11/00 an ouwr mask spaced therefrom to form an aperture ring, [he Field Search 9 central mask sized in relation to the aperture to substantially 95/12 eliminate bleeding of light at the ring of light on the drafting surface and toward the edge of the ring, during line drawing. [56] References Cited 5 Clairm, 13 Drawing Figures UNlTED STATES PATENTS 2,830,491 4/ 1958 Domeshek .355/67 PAIENTEDFEB 15 I972 3.641.885

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AUTOMATIC DRAFTING USING PROJECTED RING OF LIGIIIT BACKGROUND OF THE INVENTION This invention relates generally to automatic drafting, and more particularly concerns improvements in photoexposure devices used in conjunction with carriages movable relatively over drafting surfaces.

The use of photoexposure devices in conjunction with movable carriages, as for example in automatic indicia marking machines, such as drafting apparatus, is well known. Such devices utilize the well-known technique of directing a narrow beam of light at a photosensitive surface to expose that surface in accordance with beam movement relative to the surface for forming indicia of various sorts, one example being lines.

A serious problem that exists in photoexposure indicia forming devices consists in nonuniform exposure at the plane of the photosensitive surface and during relative movement of the beam and that surface. For example, if a circular spot of light could be uniformly illuminated, and such a spot were moved relatively over the surface in a given direction, it would be found that surface increments over which the center of the spot moves would be exposed to the beam for a much longer time interval than surface increments over which only the edge portion of the spot moves.

Actually most optical systems will have a very sharp fall-off in illumination from center to edge of a circular spot (ideally this will vary as the fourth power of the cosine of the angle between the light ray and the optical axis). This effect, when combined with the aforementioned one, makes it impossible to expose a line with a moving spot with any acceptable degree of uniformity. The edges of the line will either be seriously underexposed or the center will be severely overexposed. In the former situation, the edges becorne ragged and uncertain; in the latter bleeding from the center to edge will again give an uncertain width to the effectively exposed portion of the line.

It is the intent of this invention to minimize this uncertainty. In this regard, the optical system is such that the center to edge ratio of illumination intensity is considerably less than that normally obtainable, and the gradient of illumination intensity near the edge is much sharper. Also incorporated in this invention is the concept that by using a suitable masking or other device the central illumination can be still further reduced so that an acceptablyuniform exposure across the width of the line may be obtained, and the physical properties of the exposed area thus enhanced.

The need for this improvement becomes acute when it is desired to vary the degree of exposure of the surface to incident light as a function of the speed of movement of the spot over the surface, since the variation of exposure across the width of the line is independent of such speed, so that maintenance of proper exposure values at various speeds becomes increasingly difficult with higher speeds of travel.

SUMMARY OF THE INVENTION It is a major object of the invention to overcome the abovedescribed problems through the provision of automatic drafting apparatus in which a ring of light is projected for exposing a photosensitive drafting surface. Basically, the invention comprises a head adapted to overlie such a surface, the head being movable relative to and generally parallel to the surface; a source of light at the head; and means on the head to direct light from the source to form a ring of light at that surface during relative movement of the head and surface. As will be seen, the ring of light may be formed by mask structure in the light beam path, a mask being centered in that path to blank the center light, or the optical system itself may provide for substantial reduction of central light transmission; further, means may be provided to vary the overall size of the ring at the photosensitive surface, as will be described, in order to enable drawing lines of different widths, and the optical system is typically operable to transmit light through such different sized apertures in such manner that the illuminance of the outer edge of the ring of light in the plane of the light sensitive surface is essentially unchanged as the overall size of the apertures moved into the light path changes. For present purposes, illuminance" is defined as the luminous flux incident upon a unit area.

It is another object of the invention to provide for projection of a ring of light so dimensioned as to achieve maximum illuminance with minimum differential exposure of areal increments of the photosensitive surface over which the light ring travels. As will be seen, this object is attained when the radial distance between the inner and outer circumferences of the ring of light is about one fourth the radius of the outer circumference of the ring. Finally, it is an object of the invention to enable use of an electric are light source productive of a bright spot of light transmitted along an optical axis, with a mask located to mark out the bright spot of light.

These and other objects and advantages of the invention, as well as the details of illustrative embodiments, will be more fully understood from the following detailed description of the drawings, in which:

DRAWING DESCRIPTION FIG. 1 is a perspective showing of an automatic drafting machine in which the invention may be embodied;

FIG. 2 is a vertical elevation, taken in section through a photoexposure device usable in the FIG. 1 machine;

FIG. 3 is a schematic showing of carriage actuation and movement;

FIG. 4 is a section taken on line 44 of FIG. 2;

FIG. 5 is a section taken on line 5-5 of FIG. 2;

FIG. 6 is a perspective view showing a mask arrangement;

FIG. 7 is an optical layout;

FIG. 8 is a perspective showing of differential exposure of a photosensitive surface to a moving light spot;

FIG. 9 is a perspective showing of exposure of a photosensitive surface to a moving light ring;

FIGS. 10 and 1 l are plan views of a moving spot and ring of light;

FIG. 12 is a plan view of a ring of light of preferred proportioning; and

FIG. 13 is a block diagram of control apparatus for line width selection apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. 1 and 3, the illustrated drafting table 10 includes a flat drafting area 11 on which a sheet 11a is retained, as for example by vacuum applied from beneath. Carried on the table are a carriage l2 movable in the X- direction, and a carriage l3 movable in the Y-direction. Appropriate guides 14 for the X-carriage are located within the housing 15 and 16, and suitable antifriction rollers may be provided to support the carriage in such guides. Similar guides and rollers may be provided for Y-carriage movement along the X-carriage, and in the Y-direction.

Referring now to FIG. 3, a pinion l7 driven by servomotor 18 is shown engaging a rack 19 within the housing 16, for moving the X-carriage in the X-direction. Similarly, a pinion 20 driven by the servomotor 21 engages a rack 22 extending in the Y-direction. A control indicated at 23 in FIG. 3 controls operation of the motors to cause the head 24 in the carriage 13 to move in a precisely controlled manner over the drafting surface. In this regard, X-Y movement of an optical head over a marking or drafting surface is known, as for example is described in U.S. Pat. No. 3,120,577 to Young.

Control 23 may also embody circuitry to control operation of the head 24, and the latter may be removably mounted on I the carriage, with appropriate electrical connection made from the control to the mounted head.

In accordance with the invention, there is a source of light at the head, as for example the arc source 30 seen in FIGS. 1 and 7; further, means is provided in the head 24 to direct light from the source to form a ring of light at the photosensitive surface during relative movement of the head and that surface. In this regard, reference is made to FIGS. 8-12 in explanation of the differences is made of operation and result as between a spot" of light as used in the prior art and a ring of light as provided by the present invention.

As seen in FIG. 8, a moving spot 31 of light produces an exposed line 32 having edges 33 which are not sharp but rather uneven or fuzzy." This is caused by bleeding" of light from the inner regions of the spot toward its circular edge 34 which is likewise not sharp, but rather fuzzy." The light intensity increases toward the center of the spot, as indicated by the vertical intensity plot or graph 35 extending transversely over the spot. In particular, the arc light source produces a spot which is brightest at its center, as shown at 36, and light from that center bleeds radially toward the edge of the spot, enhancing the lack of uniformity of the exposed line edges 33. Furthermore, as seen in FIG. 10, as the spot moves in the direction of arrow X, those portions of the photosensitive surface over which the center of the spot passes receive much more exposure than is received by those portions of the surface transversed by the outer portions 37 of the spot. This is made clear by comparison of the decreasing lengths of lines a e, across the spot and corresponding to the varying degrees of exposure of surface increments under such lines. As a result, the surface increment under line a, is overexposed and increments under lines :2 are underexposed.

As contrasted with the above, FIG. 9 shows light ring 40 producing an exposed line 41 having edges 42 which are sharp. Very little if any light bleeding toward the ring edge 43 occurs, due to the reduced light intensity in the area 44 within the ring. This is illustrated by the fall off at 45 of the light intensity plots 46 taken transversely across the ring. Such reduction in light intensity in area 44 may be effected by masking as will be described, or by the optical system itself. Furthermore, as seen in FIG. 11, as the ring 40 moves in the X-direction, those portions of the photosensitive surface over which the center of the ring travels receive about the same exposure as received by those portions of the surface transversed by the outer portions 48 of the ring. This is made evident by comparison of the lengths of lines a -e across the ring and corresponding to the varying degrees of exposure of surface increments under such lines. For example, the sum of the two lines Vza and 16 a is about equal to the length of line e As a result, the surface increments that pass relatively under lines a and e-,, are properly exposed and to about the same extent.

FIG. 12 illustrates a ring of light of preferred proportioning, with the radial dimension of the ring between inner and outer circumferences equal to about AR, where R is the overall radius of the outer circumference of the ring. This configuration provides for maximum illumination with minimum differential exposure of surface increments transversed by the ring and with maximum exposed line edge Sharpeners.

Referring now to the optical system shown in FIGS. 2 and 7, light from the arc lamp source 30 is reflected by mirror 50 and passed to mirror 51 via first and second planoconvex condenser lens 52 and 53, and a condenser trimmer lens 54. These elements are enclosed within a housing 55 and suitably supported as at 56-60 as seen in FIG. 2, the optical axis being designated at 61. The housing is in turn supported on the carriage 13 that is movable in the Y-direction as described above. A removable tongue and groove vertical connection of the housing to the carriage indicated at 62 enables ready removal of the head 24 when desired. A micrometer-type height adjustment for the head 24 relative to the carriage is seen at 120. A shim gage element 121 may be placed under the lower end of the micrometer tip 122, and on the paper 11a, for assuring proper height adjustment.

From the mirror, the condensed light from the source is imaged at 63, from which a trim aperture element 64 is offset. (Light is shown passing through the mirror 51 in FIG. 7, for simplicity.) Passing beyond the element 64, the light may, if

desired, be subjected to modulation at control element 67, by

means of which the amount of light passing to planoconvex relay lenses 65 and 66 may be regulated, as for example in accordance with the movement or position of the light ring relative to the photosensitive surface indicated at 110. In this regard, U.S. Pat. No. 3,316,348 to I-Iufnagel discloses such regulation as a function of speed, andU.S. Pat. No. 3,120,577 to Young disclosed the concept of such light modulation in a recording system involving X-Y movement. A suitable actuator for element 67 is indicated at 68.

Leaving the lens 66, the light is directed to fall on a mask 70 which obstructs passage of all the light excepting for a ring of predetermined size. As seen in FIGS. 4 and 6, the mask may be defined by a transparent sheet or film 71 which is darkened centrally at 72 and concentrically at 73, leaving only the transparent annular portion 74 to pass the ring of light. A series of such sheets configured to define light rings of different size may be mounted and centered over circularly spaced apertures 75 in a turret disc 76, as by means of fasteners 77, so that outer darkened regions 73 extend to the aperture boundaries. In this regard, the use of light masks and apertures arranged on movable supports is disclosed in U.S. Pat. No. 3,306,176 to Myers, and U.S. Pat. No. 3,292,485 to Mey. Further, should the optical system itself produce the light ring, the central mask 72 may be omitted.

After passing through the mask, the ring of light is transmitted to the objective lens unit at for image projection on the photosensitive sheet 110. A shutter mechanism 81 is located at the incident side of the objective lens for controlling light transmission in such manner that the ring of light is transmitted only during predetermined intervals, as during carriage movement, whereby overexposure of the photosensitive sheet may be avoided. The shutter illustrated in FIG. 5 includes a light blanking arm 82 pivoted at 83 to structure 84, to move into and out of the light beam indicated at 85. Solenoid actuators 86 and 87 are connected at 88 and 89 to the arm to pivot same into and out of the light beam path as commanded by the control 23.

Referring to FIGS. 2,4 and 13, control means is provided to rotate the disc 76 to bring a selected mask into predetermined position in the path of the light beam. That control means may typically include an actuator such as servomotor 90 having drive connection to the turret disc 76 via coupling 91. The control also includes sensing apparatus connected to sense the extent of such rotation of the disc and to effect stoppage of the servomotor in response to turret rotation to bring a selected size mask (or aperture in the case where masks are not used) into the light beam path. Typical of such sensing apparatus is a position transducer as for example a rotary potentiometer or encoder 92 indicated in FIGS. 2 and 13. As the motor 90 rotates disc 76, a corresponding analog signal is generated by the encoder for transmission at 93 for comparison with the mask selection command analog signal at 94.

Mask selection digital signals are generated at 95 and converted at 96 to the analog signal 94. Any difference between signals 93 and 94 is detected by the comparator 97 whose corresponding output error signal E is transmitted at 98 and via the operational amplifier 99 and power amplifier 100 to drive the servomotor 90 until the error signal is eliminated, at which time the selected mask has been brought into the light beam path, as described.

In addition, latching means is operable to block rotation of disc 76 during use of the projected ring of light for line drawing purposes. As seen in FIGS. 2,4 and 13, the latching means includes keeper slots rotatable with the disc 76 and with angular spacing corresponding to the angular spacing of the various masks 70 on the disc. The latching means also includes a latch 111 controlled at 112 as by solenoid 113 to advance into a keeper slot when the error signal at 98 (and sensed by control 112) has'dropped to a low level indicating that the disc has brought a selected mask into predetermined position in the path of the light beam.

As mentioned previously, the optical system may be such that, in the absence of the mask, the center to edge ratio of illumination-intensity at the surface 11a is considerably less than that normally obtainable, and the gradient of illumination intensity near the edge is much sharper than normally obtainable. These effects may be produced through carefully balanced use of spherical aberration and the introduction of so-called pincushion distortion."

Iclaim:

1. In a drafting machine, the combination comprising:

a head adapted to overlie a photosensitive surface, said head being moved relative to and generally parallel to said surface,

a source of light at the head,

and means on the head directing light from said source and forming a ring of light at said surface during said relative movement of the head and surface, the ring characterized in that the illumination intensity within the ring substantially exceeds the illumination intensity inside a circular zone formed inwardly of the ring and at the optical axis defined by the ring,

said means including a central mask at said axis and an outer mask spaced therefrom to define a ring-shaped aperture, said central mask sized in relation to said aperture to substantially eliminate bleeding of light at said surface toward the edge of the ring during said relative movement, said ring of light having an inner boundary defined by an inner circumference and an outer boundary defined by an outer circumference, the radial distance between said inner and outer circumferences being about one-fourth the radius of the outer circumference.

2. The combination of claim 1 including structure defining a series of ring shaped apertures selectively movable into the path of light from said source, said apertures having different overall sizes, said structure including, for each ring-shaped aperture, a central circular light mask and an outer light mask having an inner edge concentrically spaced from said central mask.

3. The combination of claim 2 including a rotary disc mounting said inner and outer masks at circularly spaced locations.

4. The combination of claim 1 wherein said source comprises an electric are producing a bright spot of light transmitted along an optical axis, said central mask located to mask out said bright spot of light.

5. The combination of claim 1 wherein said last named means includes, in the light path between said source and said mask, condenser lens means for imaging said source, a light modulator and relay lens means; and, in the light path beyond said mask, a shutter and objective lens means. 

1. In a drafting machine, the combination comprising: a head adapted to overlie a photosensitive surface, said head being moved relative to and generally parallel to said surface, a source of light at the head, and means on the head directing light from said source and forming a ring of light at said surface during said relative movement of the head and surface, the ring characterized in that the illumination intensity within the ring substantially exceeds the illumination intensity inside a circular zone formed inwardly of the ring and at the optical axis defined by the ring, said means including a central mask at said axis and an outer mask spaced therefrom to define a ring-shaped aperture, said central mask sized in relation to said aperture to substantially eliminate bleeding of light at said surface toward the edge of the ring during said relative movement, said ring of light having an inner boundary defined by an inner circumference and an outer boundary defined by an outer circumference, the radial distance between said inner and outer circumferences being about one-fourth the radius of the outer circumference.
 2. The combination of claim 1 including structure defining a series of ring shaped apertures selectively movable into the path of light from said source, said apertures having different overall sizes, said structure including, for each ring-shaped aperture, a central circular light mask and an outer light mask having an inner edge concentrically spaced from said central mask.
 3. The combination of claim 2 including a rotary disc mounting said inner and outer masks at circularly spaced locations.
 4. The combinatiOn of claim 1 wherein said source comprises an electric arc producing a bright spot of light transmitted along an optical axis, said central mask located to mask out said bright spot of light.
 5. The combination of claim 1 wherein said last named means includes, in the light path between said source and said mask, condenser lens means for imaging said source, a light modulator and relay lens means; and, in the light path beyond said mask, a shutter and objective lens means. 